Childhood psychiatric disorders demonstrate a discernable developmental chronology; certain juvenile anxiety disorders typically onset earlier than behavioral disorders, which typically onset earlier than affective disorders. Childhood anxiety disorders therefore represent one of the earliest expressions of psychopathologic risk. The relevance of early onset anxiety disorders for consequent juvenile and adult mental health is, however, poorly understood. Developmental genetic epidemiology provides a framework for identifying the continuities and discontinuities in genetic and environmental risk factor effects on the chronology of comorbidity by exploiting the information contained in the pattern of disorder overlap within and across time, within individuals and between relatives of different ages. We plan to analyze longitudinal data already collected at personal interview with a large population-based sample of juvenile twins and their parents to develop a detailed understanding of the developmental genetic epidemiology of the more common juvenile anxiety disorders (separation anxiety, overanxious disorder, phobias). Analyses of multi-wave data collected from an epidemiologic sample of twin-families will permit identification of (1) the genetic, familial environmental and individual-specific environmental influences on transient versus persistent disorder, (2) the continuity or discontinuity of these risk factors with those for contemporaneous and consequent risk for other anxiety, behavioral and affective disorders, and (3) the maternal and paternal psychiatric disorders associated with the familial transmission of risk. Identification of the genetic and environmental risk factors that underlie developmental trajectories and endpoints of early juvenile psychopathology will guide intervention and prevention efforts designed to minimize the progression and chronicity of mental disorders.